An image sensor is a device that can convert an optical image into an electronic signal. Image sensors are oftentimes utilized in still cameras, video cameras, video systems, and other imaging devices. Cameras and other imaging devices commonly employ either a charge-coupled device (CCD) image sensor or a complementary metal-oxide-semiconductor (CMOS) image sensor.
CMOS image sensors include an array of pixels, each of which can comprise a photodetector. CMOS image sensors also include circuitry to convert light energy to an analog voltage and additional circuitry to convert the analog voltage to digital data. A CMOS image sensor can be an integrated circuit (e.g., a system on chip (SoC)) that includes various analog, digital, and/or mixed-signal components for capturing light and processing imaging related information. For example, components integrated into the CMOS image sensor oftentimes include a processor module (e.g., microprocessor, microcontroller, or digital signal processor (DSP) core), memory, analog interfaces (e.g., analog-to-digital converters, digital-to-analog converters), and so forth.
Visible imaging systems implemented using CMOS image sensors can reduce costs, power consumption, and noise while improving resolution. For instance, cameras can use CMOS image sensors that efficiently marry low-noise image detection and signal processing with multiple supporting blocks that can provide timing control, clock drivers, reference voltages, analog to digital conversion, digital to analog conversion, key signal processing elements, and the like. High-performance video cameras can thereby be assembled using a CMOS integrated circuit supported by few components including a lens and a battery, for instance. Accordingly, by leveraging CMOS image sensors, camera size can be decreased and battery life can be increased. Also, dual-use cameras have emerged that can employ CMOS image sensors to alternately produce high-resolution still images or high definition (HD) video.
When capturing an image of a scene using an image sensor, lighting conditions can vary. For instance, the scene may be too dark, too light, too diverse, or too dynamic, such as when a cloud quickly blocks the sun. To adjust to different lighting conditions, it is desirable to have an image sensor with a wide dynamic range, where the image sensor can adjust to current lighting conditions to enhance details in the image. Yet, dynamic ranges of many conventional image sensors are oftentimes not high enough, which leads to these image sensors being unable to capture some details in a scene. By way of illustration, some traditional image sensors, when capturing an image of an outdoor scene in bright light, may be unable to satisfactorily render a portion of the scene in a shadow (e.g., details of the scene in the shadow may be rendered as pitch black) and/or a portion of the scene in high light (e.g., details of the scene in high light may be rendered as white) due to the typical dynamic ranges of such traditional image sensors.